The present invention relates to an oil pressure rush adjuster to be used for a valve actuating mechanism in an internal combustion engine, in which a space or a clearance formed at the valve is automatically rectified or corrected, particularly to an oil pressure lash adjuster equipped with an air vent which is capable of smoothly mounting the main body (or main assembly) of the lash adjuster to a rush adjuster mounting hole.
A valve actuating mechanism to be used in an internal combustion engine is generally liable to be subjected to the influence of wear or thermal expansion, so that a space or clearance formed at the valve used in the mechanism may be changed during the operation thereof. Accordingly, an oil pressure lash adjuster has been used so as to rectify or correct the above space or clearance.
As shown in FIG. 7, a conventional oil pressure rush adjuster has a structure such that a main body 2 of the lash adjuster (hereinafter referred to as "adjuster main body") is mounted to a mounting hole 30 formed in a cylinder head 10. The adjuster main body 2 comprises a body 24 and a plunger 26 which is arranged in the body 24 so that it is slidable in the upward and downward directions. In the plunger 26, there is formed a reservoir 28 which communicates with an oil gallery 32 which opens in the mounting hole 30 through small holes 24b and 27a. The reservoir 28 communicates with a high pressure chamber 29 through a small hole 27b. The reservoir 28 and the high pressure chamber 29 are filled with an actuating oil which is supplied from the oil gallery 32. In FIG. 7, the reference numerals 14, 16 and 17 denote a valve member, a cam and a rocker arm, respectively, which are members constituting the valve actuating mechanism. When a pressure is applied to the actuating oil, a check ball 25a disposed in the high pressure chamber 29 blocks the small hole 27b and the plunger 26 in a locked state constitutes a swinging supporting point for the rocker arm 17. In addition, when a nose 16a of the cam presses to rocker arm 17, the locker arm 17 is swung so that the valve member 14 is slid against a restoring spring 15 to be opened. Thereafter, when the cam 16 is rotated, the valve member 14 is closed under the action of the restoring spring 15. The reference numeral 23 denotes a plunger spring. The plunger 26 is always kept in a state such that it is caused to contact the rocker arm 17 under the action of the plunger spring 23. The plunger 26 is operated so that it corrects the space or clearance formed in the valve actuating mechanism due to the thermal deformation thereof, and the occurrence the space or clearance is prevented. In addition, in the cylinder head 10, there is formed an air vent 4 which extends from the mounting hole 30 to the ambient air, and the air vent 4 may function as an air vent when the adjuster main body 2 is inserted into the mounting hole 30. More specifically, when the adjuster main body 2 is intended to be mounted to the mounting hole 30, the adjuster main body 2 which has been disposed above the mounting hole 30 is inserted into the mounting hole 30. At this time, the air contained in the mounting hole 30 is discharged through the air vent 4 so that the insertion of the adjuster main body 2 is not prevented. As a result, it is possible to insert the adjuster main body 2 into the mounting hole 30. However, in the conventional oil pressure lash adjuster as described above, there is provided the air vent 4 which extends from the inside of the mounting hole 30 to the ambient air. Accordingly, when the internal combustion engine is stopped, the actuating oil filling the reservoir 28 and the oil gallery 32 is passed through the clearance between the body 24 and the mounting hole 30 and leaks out through the air vent 4 toward the outside of the mounting hole 30. Accordingly, the oil level is lowered to a position denoted by H in FIG. 7. In such a case, when the engine is restarted, etc., and the actuating oil is drawn from the reservoir 28, the air disposed above the oil level can simultaneously be drawn into the high pressure chamber 29 together with the actuating oil. Particularly, when the internal combustion engine is stopped while the cam nose 16a is caused to contact the rocker arm 17, the plunger 26 is compressed and is in a most shortened state (or bottomed condition). If the engine is restarted under the above condition, the sliding stroke between the plunger 26 and the body 24 becomes maximum, and the amount of the actuating oil drawn into the high pressure chamber 29 also becomes maximum. However, since the actuating oil is not supplied from the internal combustion engine side while the engine is stopped, it is almost impossible to ensure the proper amount of the oil contained in the reservoir 28. As a result, in such a case, the air is drawn into the high pressure chamber 29 most drastically, when the engine is restarted. When the air is drawn into the high pressure chamber 29, the rigidity of the actuating oil which is to be generated in the high pressure chamber 29 when the plunger 26 is pressed, is extremely reduced so that a sponge condition is provided. As a result, the space or clearance of the valve cannot be rectified. In addition, when an internal combustion engine is driven while the actuating oil is supplied to the reservoir 28, the actuating oil leaks out through the air vent 4 through the same passage through which the actuating oil leaks out at the time of the stoppage of the internal combustion engine as described above, whereby the actuating oil is wastefully consumed. When the actuating oil is wastefully consumed, it is possible that the oil is not sufficiently supplied to the parts such as the metal constituting the crank shaft and the cam shaft, etc., to which the oil is to be supplied, and the seizure (or seizing) thereof occurs. Further, there can also be posed a problem such that a pump having a large capacity is required in view of the amount of the oil which can leak out.